Isaku Yamahata
2008-Jun-10 07:35 UTC
[PATCH] xen: Use wmb instead of rmb in xen_evtchn_do_upcall().
This patch is ported one from 534:77db69c38249 of linux-2.6.18-xen.hg.
Use wmb instead of rmb to enforce ordering between
evtchn_upcall_pending and evtchn_pending_sel stores
in xen_evtchn_do_upcall().
Cc: Samuel Thibault <samuel.thibault at eu.citrix.com>
Signed-off-by: Isaku Yamahata <yamahata at valinux.co.jp>
---
drivers/xen/events.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index 73d78dc..332dd63 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -529,7 +529,7 @@ void xen_evtchn_do_upcall(struct pt_regs *regs)
#ifndef CONFIG_X86 /* No need for a barrier -- XCHG is a barrier on x86. */
/* Clear master flag /before/ clearing selector flag. */
- rmb();
+ wmb();
#endif
pending_words = xchg(&vcpu_info->evtchn_pending_sel, 0);
while (pending_words != 0) {
--
1.5.3
Nick Piggin
2008-Jun-10 07:41 UTC
[PATCH] xen: Use wmb instead of rmb in xen_evtchn_do_upcall().
On Tuesday 10 June 2008 17:35, Isaku Yamahata wrote:> This patch is ported one from 534:77db69c38249 of linux-2.6.18-xen.hg. > Use wmb instead of rmb to enforce ordering between > evtchn_upcall_pending and evtchn_pending_sel stores > in xen_evtchn_do_upcall().There are a whole load of places in the kernel that should be using smp_ variants of memory barriers. This seemed to me like one of them, but I could be wrong. Also, if you do that can you get rid of the ifdef? If it really *really* mattered, we could introduce smp_mb before/after xchg... but if you use smp_wmb anyway then it definitely does not matter because that is a noop on x86. Thanks, Nick>Cc: Samuel Thibault <samuel.thibault at eu.citrix.com>> Signed-off-by: Isaku Yamahata <yamahata at valinux.co.jp> > --- > drivers/xen/events.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/drivers/xen/events.c b/drivers/xen/events.c > index 73d78dc..332dd63 100644 > --- a/drivers/xen/events.c > +++ b/drivers/xen/events.c > @@ -529,7 +529,7 @@ void xen_evtchn_do_upcall(struct pt_regs *regs) > > #ifndef CONFIG_X86 /* No need for a barrier -- XCHG is a barrier on x86. > */ /* Clear master flag /before/ clearing selector flag. */ > - rmb(); > + wmb(); > #endif > pending_words = xchg(&vcpu_info->evtchn_pending_sel, 0); > while (pending_words != 0) {